Network Working Group C. Allocchio
Request for Comments: 3192 GARR-Italy
Obsoletes: 2304 October 2001
Updates: 2846
Category: Standards Track
Minimal FAX address format in Internet Mail
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This memo describes a simple method of encoding Global Switched
Telephone Network (GSTN) addresses of facsimile devices in the
local-part of Internet email addresses.
1. Introduction
As with all Internet mail addresses, the left-hand-side (local-part)
of an address generated according to this specification, is not to be
interpreted except by the MTA that is named on the right-hand-side
(domain).
Since the very first e-mail to fax gateway objects appeared, a number
of different methods to specify a fax address as an e-mail address
have been used by implementors. Several objectives for this methods
have been identified, like to enable an e-mail user to send and
receive faxes from his/her e-mail interface, to allow some kind of
"fax over e-mail service" transport (possibly reducing the costs of
GSTN long distance transmissions) while using the existing e-mail
infrastructure.
This memo describes the MINIMAL addressing method and standard
extensions to encode FAX addresses into e-mail addresses, as required
in reference [13]. The opposite problem, i.e., to allow a
traditional numeric-only fax device user to access the e-mail
transport service, is not discussed here.
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These IANA forms used to register the standard elements defined here
are given in the "IANA Considerations" chapter (section 7 of this
document).
All implementations supporting FAX over e-mail address format MUST
support this minimal specification.
1.1 Terminology and Syntax conventions
In this document the formal definitions are described using ABNF
syntax, as defined into [7]. We will also use some of the "CORE
DEFINITIONS" defined in "APPENDIX A - CORE" of that document. The
exact meaning of the capitalized words
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", "OPTIONAL"
is defined in reference [6].
In this document the following new terms are also defined:
I-fax device:
an I-pstn device type [13] which is able to communicate either
directly or indirectly with the traditional FAX over GSTN
service;
mta-I-fax:
the Internet domain name which identifies uniquely an I-fax
device over the Internet (see also mta-I-pstn in [13]);
fax-email:
the complete Internet e-mail address structure which is used to
transport a FAX address over the Internet e-mail service (see
also pstn-email in [13]).
2. Minimal Fax address
The minimal fax address within e-mail has been defined for
consistency with reference [13] and it contains two elements: the
fax-mbox and an optional qualif-type1 element.
More precisely the GSTN minimal address specification requires the
use of a unique service-selector for each specific application
(section 2 in [13]).
The "service-selector" defined for the fax service is as follows:
service-selector = "FAX"
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In the syntax for the fax address a qualif-type1 element has been
defined for support of T.30/T.33 subaddresses (see section 2 of
[13]). The use of this element is OPTIONAL, but compliant
implementations MUST be able to support and correctly interpret it
when present. Its definition is as follows:
qualif-type1 = "/" t33-sep "=" sub-addr
where
t33-sep = "T33S"
sub-addr = 1*( DIGIT )
Thus, the minimal specification of a fax in e-mail address is:
fax-address = fax-mbox [ "/T33S=" sub-addr ]
fax-mbox = "FAX=" global-phone
Notes:
For the case of a single subaddress, only numbers are allowed in
which is consistent with T.30, T.33, and this document.
While T.30 and T.33 use SPACE to pad its field, padding isn't
necessary in the field defined by this document.
For the case of multiple subaddresses, T.33 specifies the "#"
character be used to specify multiple subaddreses. However, only
digits are permitted in the field defined by this
document. Refer to section 4.1 in case multiple per
per need to be specified.
The Minimal supported syntax for global-phone (as described in
section 2.1 of reference [13]) is:
global-phone = "+" 1*( DIGIT / written-sep )
written-sep = ( "-" / "." )
Refer to section 2.1 in [13] for other important considerations about
the global-phone element.
2.2 Some examples of a minimal "fax-address"
Some examples of minimal fax-address follows:
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FAX=+3940226338
FAX=+12027653000/T33S=1387
FAX=+33-1-88335215
Note:
the examples shown are just for illustration purposes.
3. The e-mail address of the I-fax device: mta-I-fax
An "I-fax device" has, among its characteristics, a unique Internet
domain name which identifies it on the Internet. Within Internet
mail, this is the Right Hand Side (RHS) part of the address, i.e.,
the part on the right of the "@" sign. For purposes of this document
we will call this "mta-I-fax"
mta-I-fax = domain
For "domain" strings used in SMTP transmissions, the string MUST
conform to the requirements of that standards specifications
[1], [3]. For "domain" strings used in message content headers, the
string MUST conform to the requirements of the relevant standards
[2], [3].
Note:
the use of "domain names" or "domain literals" is permitted in
addresses in both the SMTP envelope and message header fields.
4. The fax-email
The complete structure used to transfer a minimal FAX address over
the Internet e-mail transport system is called "fax-email". This
object is a an e-mail address which conforms to [2] and [3]
"addr-spec" syntax, with structure refinements which allows the FAX
number to be identified.
fax-email = ["""] ["/"] fax-address ["/"] ["""] "@" mta-I-fax
Implementors' note:
The optional "/" characters can result from translations from
other transport gateways (such as some X.400 gateways) which have
included the "/" as an optional element. Implementations MUST
accept the optional slashes but SHOULD NOT generate them.
Gateways are allowed to strip them off when converting to Internet
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mail addressing. The relevant standard [2], [3] define exactly
when the optional "quotes" characters surrounding the entire local
part (i.e., the part on the left of the "@" character into the
fax-email) MUST be added.
4.1 Multiple subaddresses
There are some instances in GSTN applications where multiple
subaddresses are used: T.33 subaddresses in fax service are one of
these cases. In e-mail practice a separate and unique e-mail address
is always used for each recipient; as such, if multiple T.33
subaddresses are present, the use of multiple "fax-email" elements is
REQUIRED.
Implementors' note:
The UA MAY accept multiple subaddress elements for the same
global-phone, but it MUST generate multiple "fax-mbox" elements
when submitting the message to the MTA.
4.2 Some examples of minimal "fax-email"
Some examples of minimal fax-email addresses follows:
FAX=+3940226338@faxworld.org
FAX=+12027653000/T33S=1387@faxworld.org
/FAX=+33-1-88335215/@faxworld.org
Note:
the examples shown are just for illustration purposes.
5. Conclusion
This proposal creates a minimal standard encoding for FAX addresses
within the global e-mail transport system. The proposal is
consistent with existing e-mail standards.
6. Security Considerations
This document specifies a means by which FAX addresses can be encoded
into e-mail addresses. Since e-mail routing is determined by Domain
Name System (DNS) data, a successful attack to DNS could disseminate
tampered information, which causes e-mail messages to be diverted via
some MTA or Gateway where the security of the software has been
compromised.
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There are several means by which an attacker might be able to deliver
incorrect mail routing information to a client. These include: (a)
compromise of a DNS server, (b) generating a counterfeit response to
a client's DNS query, (c) returning incorrect "additional
information" in response to an unrelated query. Clients SHOULD
ensure that mail routing is based only on authoritative answers.
Once DNS Security mechanisms [5] become more widely deployed, clients
SHOULD employ those mechanisms to verify the authenticity and
integrity of mail routing records.
7. IANA Considerations
The IANA registration forms for "FAX" service-selector and "T33S"
qualif-type1 elements are defined here. These forms update the
previous registration forms defined in [15].
7.1 IANA Registration form for updated value of GSTN
address service-selector "FAX"
To: IANA@iana.org
Subject: Registration of updated values for the GSTN address
service-selector specifier "FAX"
service-selector name:
FAX
Description of Use:
FAX - specify that the GSTN address refers either to an
Internet Fax device, or an onramp/offramp Fax gateway.
For a complete description refer to RFC 3192 and RFC 3191.
Security Considerations:
See the Security Consideration section of RFC 3192.
Person & email address to contact for further information:
Claudio Allocchio
INFN-GARR
c/o Sincrotrone Trieste
SS 14 Km 163.5 Basovizza
I 34012 Trieste
Italy
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RFC2822: Claudio.Allocchio@garr.it
X.400: C=it;A=garr;P=garr;S=Allocchio;G=Claudio;
Phone: +39 040 3758523
Fax: +39 040 3758565
7.2 IANA Registration form for updated value of GSTN
address qualit-type1 keyword "T33S" and value
To: IANA@iana.org
Subject: Registration of updated values for the GSTN address
qualif-type1 element "T33S"
qualif-type1 "keyword" name:
T33S
qualif-type1 "value" ABNF definition:
sub-addr = 1*( DIGIT )
Description of Use:
T33S is used to specify the numeric only optional fax sub-address
element described in "ITU T.33 - Facsimile routing utilizing the
subaddress; recommendation T.33 (July, 1996)". Further detailed
description is available in RFC 3192.
Use Restriction:
The use of "T33S" is restricted to "FAX" service-selector, is it
has no meaning outside the fax service.
Security Considerations:
See the Security Consideration section of RFC 3192.
Person & email address to contact for further information:
Claudio Allocchio
INFN-GARR
c/o Sincrotrone Trieste
SS 14 Km 163.5 Basovizza
I 34012 Trieste
Italy
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RFC2822: Claudio.Allocchio@garr.it
X.400: C=it;A=garr;P=garr;S=Allocchio;G=Claudio;
Phone: +39 040 3758523
Fax: +39 040 3758565
8. Changes since RFC 2304 specification
Although there are no major or technical changes from RFC 2304
specification, this section briefly describes where updates and
clarifications were introduced:
- considering the case that telephony systems do not conform any
more to the "single/few" Public Operator paradigm, the old
definition "PSTN - Public Switched Telephone Network" was changed
into the more adequate "GSTN - Global Switched Telephone Network"
one. However, in order to remain consistent with the previous
specification, the ABNF variables names were not changed.
- section 7 "IANA Considerations" and the IANA registration forms
for the "FAX" "service-selector" and for the "T33S" "qualif-type1"
elements were added;
- an explicit list of "new terms" with explanations was added to
section 1.1;
- the case when multiple T.33 subaddresses are present was described
more explicitly in order to clarify how to handle them (section
4.1);
- in section 3 the language describing "mta-I-fax" was updated to
better describe its relationship with an Internet Mail address;
- in section 4., the quoting rules of the "fax-address" and their
practical use was made explicit both in the definition of "fax-
email" and in the Implementors' note;
- the Author's Address was updated;
- the References list was updates to substitute ITU E.164 (1991)
with ITU E.164 (1997).
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9. Author's Address
Claudio Allocchio
INFN-GARR
c/o Sincrotrone Trieste
SS 14 Km 163.5 Basovizza
I 34012 Trieste
Italy
RFC2822: Claudio.Allocchio@garr.it
X.400: C=it;A=garr;P=garr;S=Allocchio;G=Claudio;
Phone: +39 040 3758523
Fax: +39 040 3758565
10. References
[1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1982.
[2] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.
[3] Braden, R., "Requirements for Internet hosts - application and
support", STD 3, RFC 1123, October 1989.
[4] Malamud, C. and M. Rose, "Principles of Operation for the
TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC
1528, October 1993.
[5] Eastlake, D. and C. Kaufman, "Domain Name System Security
Extensions", RFC 2065, January 1997.
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[7] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications", RFC 2234, November 1997.
[8] ITU F.401 - Message Handling Services: Naming and Addressing for
Public Message Handling Service; recommendation F.401 (August
1992).
[9] ITU F.423 - Message Handling Services: Intercommunication
Between the Interpersonal Messaging Service and the Telefax
Service; recommendation F.423 (August 1992).
[10] ITU E.164 - The International Public Telecommunication Numbering
Plan E.164/I.331 (May 1997).
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[11] ITU T.33 - Facsimile routing utilizing the subaddress;
recommendation T.33 (July 1996).
[12] ETSI I-ETS 300,380 - Universal Personal Telecommunication (UPT):
Access Devices Dual Tone Multi Frequency (DTMF) sender for
acoustical coupling to the microphone of a handset telephone
(March 1995).
[13] Allocchio, C., "Minimal GSTN address format in Internet Mail",
RFC 3191, October 2001.
[14] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping
between X.400 and RFC 822/MIME", RFC 2156, January 1998.
[15] Allocchio, C., "GSTN address element extensions in e-mail
services", RFC 2846, June 2000.
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